Interleukin-38 (IL-38) is a member of the interleukin-1 (IL-1) family and the interleukin-36 (IL-36) subfamily. It is important for the inflammation and host defense. This cytokine is named IL-1F10 in humans and has similar three dimensional structure as IL-1 receptor antagonist (IL-1Ra). The organisation of IL-1F10 gene is conserved with other members of IL-1 family within chromosome 2q13. IL-38 is produced by mammalian cells may bind the IL-1 receptor type I. It is expressed in basal epithelia of skin, in proliferating B cells of the tonsil, in spleen and other tissues. This cytokine is playing important role in regulation of innate and adaptive immunity. [1]
IL-38 probably originated from a common ancestral gene - an ancient IL-1RN gene. [2] This cytokine has 41% homology with IL-1Ra and 43% homology with IL-36Ra. IL-38 is expressed in skin, spleen, tonsil, thymus, heart, placenta and fetal liver. [3] In tissues which do not play a special role in immune response, IL-38 is expressed in low quantity similar to other members of the IL-1 family. [4] In disease setting, specially when the activation of inflammatory response is dysregulated, the expression of IL-38 is changed. For example, in case of spondylitis ankylopoetica, [5] cardiovascular disease, [6] rheumatoid arthritis [7] or hidradenitis suppurativa. [8]
According to consensus of cleaving site of IL-1 family, it is predicted that two amino acids (AA) should be removed to generate a processed 3-152AA IL-38 protein. The protease which cleaves IL-38 is still unknown as well as it is still not known which form of IL-38 is the natural variant present in the human body. It was reported that 20-152AA IL-38 form has increased biological activity. [9]
IL-38 has non-characteristic dose-response curve and it binds to IL-36R (IL-1R6). This cytokine is blocking Candida -induced interleukin-17 (IL-17) response better in low concentration than in higher concentration even if induction of cytokine is not blocked. [10] So it is possible that IL-38 released by apoptotic cells can bind to the Three Immunoglobulin Domain-containing IL-1 receptor-related 2 (TIGIRR-2, gene name IL1RAPL1, also known as IL-1R9) and IL-38 will have in this case an antagonistic effect on induction of inflammatory cytokine. It is possible that IL-38 would be first ligand of TIGIRR-2, a former orphan receptor of the IL-1 Family. [9]
Studies showed that IL-38 could play an important role in rheumatic diseases. [11] [12] [13] IL-38 is also one of the five proteins which are related with C-reactive protein (CRP) levels in the serum. [14] The association of IL-38 with CRP could mean that IL-38 will play role also in inflammatory diseases as cardiovascular disease.
The observation of knockdown of IL-38 with siRNA in peripheral blood mononuclear cells shows that production of interleukin-6 (IL-6), APRIL and CCL-2 were increased in response to TLR ligands, so IL-38 acted like antagonist in this case. [15] There are also studies which show agonistic effect. [9] [10] [16] In one study was compared the function of full-length IL-38 and truncated IL-38 and showed that high concentrations of the truncated IL-38 decreased production of IL-6 in response to interleukin-1β (IL-1β) in human macrophages, while full-length form increased IL-6 in the same concentrations. So IL-38 could have agonistic and also antagonistic effects which depend on processing and concentration. [9]
Also when spontaneous murine model of systemic lupus erythematosus (SLE) was treated with recombinant IL-38, mice had less symptoms like proteinuria and skin lesions. [17] Also serum levels of IL-17 and interleukin-22 were lower in these mice what approves in vitro observation that IL-38 could inhibit Th17 responses. Patients with SLE had higher concentrations of IL-38 in the serum than healthy patients and also patients with active disease had higher concentrations of IL-38 in the serum than patients with inactive form. [15]
Sjogren's disease is disease related to SLE. Biopsy of gland of patients with primary Sjogren's disease shows that the expression of IL-38 was increased here. For modulation of this disease is important axis of IL-36. IL-38 is probably antagonist of IL-36 signaling similar as IL-36Ra what can play an important role in the pathogenesis of this autoimmune disease. [18]
IL-38 was found also in the synovium of patients with rheumatoid arthritis and as well in mice with collagen-induced arthritis (CIA). IL-38 concentrations correlated with IL-1β. The overexpression of IL-38 in murine model of arthritis and serum transfer-induced arthritis ameliorate these diseases but not in case of antigen-induced arthritis. TNF production and IL-17 responses were decreased in these models. These data shows that IL-38 could have anti-inflammatory properties in rheumatoid arthritis and probably could be use in a therapeutic strategy. [19]
Interleukin 10 (IL-10), also known as human cytokine synthesis inhibitory factor (CSIF), is an anti-inflammatory cytokine. In humans, interleukin 10 is encoded by the IL10 gene. IL-10 signals through a receptor complex consisting of two IL-10 receptor-1 and two IL-10 receptor-2 proteins. Consequently, the functional receptor consists of four IL-10 receptor molecules. IL-10 binding induces STAT3 signalling via the phosphorylation of the cytoplasmic tails of IL-10 receptor 1 + IL-10 receptor 2 by JAK1 and Tyk2 respectively.
Interleukin 6 (IL-6) is an interleukin that acts as both a pro-inflammatory cytokine and an anti-inflammatory myokine. In humans, it is encoded by the IL6 gene.
Interleukin-15 (IL-15) is a protein that in humans is encoded by the IL15 gene. IL-15 is an inflammatory cytokine with structural similarity to Interleukin-2 (IL-2). Like IL-2, IL-15 binds to and signals through a complex composed of IL-2/IL-15 receptor beta chain (CD122) and the common gamma chain. IL-15 is secreted by mononuclear phagocytes following infection by virus(es). This cytokine induces the proliferation of natural killer cells, i.e. cells of the innate immune system whose principal role is to kill virally infected cells.
Interleukin-18 (IL-18), also known as interferon-gamma inducing factor is a protein which in humans is encoded by the IL18 gene. The protein encoded by this gene is a proinflammatory cytokine. Many cell types, both hematopoietic cells and non-hematopoietic cells, have the potential to produce IL-18. It was first described in 1989 as a factor that induced interferon-γ (IFN-γ) production in mouse spleen cells. Originally, IL-18 production was recognized in Kupffer cells, and liver-resident macrophages. However, IL-18 is constitutively expressed in non-hematopoietic cells, such as intestinal epithelial cells, keratinocytes, and endothelial cells. IL-18 can modulate both innate and adaptive immunity and its dysregulation can cause autoimmune or inflammatory diseases.
Interleukin-26 (IL-26) is a protein that in humans is encoded by the IL26 gene.
Interleukin 24 (IL-24) is a protein in the interleukin family, a type of cytokine signaling molecule in the immune system. In humans, this protein is encoded by the IL24 gene.
Interleukin-22 (IL-22) is a protein that in humans is encoded by the IL22 gene.
Interleukin 20 (IL20) is a protein that is in humans encoded by the IL20 gene which is located in close proximity to the IL-10 gene on the 1q32 chromosome. IL-20 is a part of an IL-20 subfamily which is a part of a larger IL-10 family.
Interleukin 17 family is a family of pro-inflammatory cystine knot cytokines. They are produced by a group of T helper cell known as T helper 17 cell in response to their stimulation with IL-23. Originally, Th17 was identified in 1993 by Rouvier et al. who isolated IL17A transcript from a rodent T-cell hybridoma. The protein encoded by IL17A is a founding member of IL-17 family. IL17A protein exhibits a high homology with a viral IL-17-like protein encoded in the genome of T-lymphotropic rhadinovirus Herpesvirus saimiri. In rodents, IL-17A is often referred to as CTLA8.
The interleukin-1 receptor antagonist (IL-1RA) is a protein that in humans is encoded by the IL1RN gene.
Tyrosine-protein kinase JAK3 is a tyrosine kinase enzyme that in humans is encoded by the JAK3 gene.
Interleukin 35 (IL-35) is a recently discovered anti-inflammatory cytokine from the IL-12 family. Member of IL-12 family - IL-35 is produced by wide range of regulatory lymphocytes and plays a role in immune suppression. IL-35 can block the development of Th1 and Th17 cells by limiting early T cell proliferation.
Interleukin 17 receptor A, also known as IL17RA and CDw217, is a human gene.
Interleukin 20 receptors (IL20R) belong to the IL-10 family. IL20R are involved in both pro-inflammatory and anti-inflammatory immune response. There are two types of IL20R: Type I and Type II.
Interleukin-17A is a protein that in humans is encoded by the IL17A gene. In rodents, IL-17A used to be referred to as CTLA8, after the similarity with a viral gene.
Anti-interleukin-6 agents are a class of therapeutics. Interleukin 6 is a cytokine relevant to many inflammatory diseases and many cancers. Hence, anti-IL6 agents have been sought. In rheumatoid arthritis they can help patients unresponsive to TNF inhibitors.
The Interleukin-1 family is a group of 11 cytokines that plays a central role in the regulation of immune and inflammatory responses to infections or sterile insults.
Interleukin 36, or IL-36, is a group of cytokines in the IL-1 family with pro-inflammatory effects. The role of IL-36 in inflammatory diseases is under investigation.
Systemic-onset juvenile idiopathic arthritis (sJIA), also known as Still disease, Still's disease, and systemic juvenile idiopathic arthritis, is a subtype of juvenile idiopathic arthritis (JIA) that is distinguished by arthritis, a characteristic erythematous skin rash, and remitting fever. Fever is a common symptom in patients with sJIA, characterized by sudden temperature rise above 39C and then a sudden drop. Over 80% of patients have a salmon-colored macular or maculopapular rash, which can be migratory and nonpruritic. Arthritis can develop weeks, months, or even years after onset and can affect various joints. SJIA is characterized by splenic and lymph node enlargements, with prominent symmetrical lymphadenopathy. Pericardial involvement is common, with 81% of children with active systemic symptoms having abnormal echocardiographic findings and 36% having an effusion or pericardial thickening. Around one-third of children with sJIA have occult macrophage activation syndrome (MAS), a potentially fatal illness causing T cells and macrophages to rapidly multiply and activate, resulting in a "cytokine storm."
Interleukin 40 (IL-40), also known with other name C17orf99, is a protein belonging to a group of cytokines called interleukins. It is encoded by a gene that does not belong to any cytokine superfamily. This cytokine is produced primarily by human expression tissues such as bone marrow and fetal liver, and its expression can be also induced in peripheral B cells after activation. IL-40 is involved in immunoglobulin A (IgA) production, and plays an important role in humoral immune responses and B cell homeostasis and development.
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